Process for effecting ultra-deep HDS of hydrocarbon feedstocks

ABSTRACT

The present invention pertains to a process for reducing the sulfur content of a hydrocarbon feedstock to a value of less than about 200 ppm, comprising optionally subjecting a catalyst comprising a Group VIB metal component, a Group VIII metal component, and an S-containing organic additive to a sulfidation step and/or activation step, and contacting a feedstock with a 95% boiling point of about 450° C. or less with the optionally sulfided and/or activated catalyst under conditions of elevated temperature and pressure to form a product with a sulfur content of less than about 200 ppm, preferably less than about 50 ppm.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. ProvisionalApplication 60/237892, filed Oct. 4, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a process for effectingultra-deep HDS of hydrocarbon feedstocks.

[0004] 2. Prior Art

[0005] In an effort to regulate SO₂ emissions from the burning of fuelsand to optimise the performance of tail-end catalysts, in particularexhaust treatment catalysts, the regulations as to the sulfur content offuels, in particular diesel fuels, are becoming more and more strict. InEurope as of 2000 diesel feedstocks are required to have a sulfurcontent less than 350 ppm, while as of 2005, the sulfur content shouldbe less than 50 ppm, with even further decreases not being excluded.

[0006] In consequence, there is an increasing need for catalyst systemswhich can decrease the sulfur content of a hydrocarbon feedstock with a95% boiling point of about 450° C. or less to less than about 200 ppm,preferably less than about 100 ppm, even more preferably less than about50 ppm, calculated by weight as elemental sulfur on the total liquidproduct.

[0007] In the context of the present specification the term ultra-deepHDS means the reduction of the sulfur content of a hydrocarbon feedstockto a value of less than about 200 ppm, preferably less than about 100ppm, and even more preferably to a value of less than about 50 ppm,calculated by weight as elemental sulfur on the total liquid product, asdetermined in accordance with ASTM D-4294. The indications Group VIB andGroup VIII correspond to the Periodic Table of Elements applied byChemical Abstract Services (CAS system).

[0008] The problem associated with effecting this ultra-deep HDS is thatthe last sulfur compounds present in the feed are the hardest to remove.

[0009] Depending on their source, petroleum fractions can comprisevarious types of sulfur compounds. In hydrotreated middle distillatefractions, the major sulfur components are benzothiophenes anddibenzothiophenes. In straight-run materials significant quantities ofother components are present, such as thiophenes, mercaptanes, sulfides,and disulfides. Of these, the sulfides and disulfides are the mostreactive, followed by the thiophenes, benzothiophenes, anddibenzothiophenes. Within the group of dibenzothiophenes some componentsare more reactive than others. In consequence, in conventionalhydrodesulfurisation (HDS), in which the sulfur level is reduced to avalue of, say, about 0.3 wt. %, the sulfides and thiophenes are removed.In deep HDS, to a sulfur level of, say 200 to about 500 ppm, thebenzothiophenes are removed. To effect ultra-deep HDS to a sulfur levelof below about 200 ppm, the last compounds present, in particular alimited number of alkylated benzothiophenes, need to be removed in wholeor in part, with the alkyldibenzothiophenes which have the alkyl on the4- or 6-position being particularly difficult to remove.

[0010] It has been found that the reaction mechanisms by which thesevery refractive sulfur compounds are decomposed are different from thoseby which the less refractive compounds are decomposed. This isevidenced, e.g., by the fact that the catalysts which are known asparticularly suitable for HDS appear to function less well in ultra-deepHDS. For example, conventionally, cobalt-molybdenum catalysts are moreactive in HDS than nickel-molybdenum catalysts. However, for ultra-deepHDS it has been found that nickel-molybdenum catalysts show betterresults than cobalt-molybdenum catalysts. Reference is made to the paperentitled “Ultra low sulfur diesel: Catalyst and Process options”presented at the 1999 NPRA meeting by T. Tippet et al.

[0011] The consequence of this difference in reaction mechanisms impliesthat the refiner who is faced with having to produce material with alower sulfur content cannot just apply his usual hydrodesulfurisationcatalyst under more stringent conditions. On the contrary, he will haveto specifically select the hydrotreating catalyst that is most effectivein effecting ultra-deep HDS. This is the more so since the reactionconditions necessary to effect ultra-deep HDS are rather severe inthemselves, and the use of a dedicated catalyst makes it possible toselect less severe reaction conditions, resulting in energy saving and alonger catalyst lifespan.

[0012] Catalysts which comprise a Group VIB metal component, a GroupVIII metal component, and an S-containing organic additive are known inthemselves in the art.

[0013] For example, European patent application No. 0 300 629 andEuropean patent application No. 0 357 295 describe hydrotreatingcatalysts comprising a support impregnated with at least one member ofmolybdenum, tungsten, and/or metals of Group VIII of the Periodic Table,and a mercapto-compound selected from mercaptocarboxylic acids,amino-substituted mercaptanes, dimercaptanes, and thioacids. TheS-containing additive is incorporated into the catalyst composition toobviate the necessity of presulfiding, or to at least make thepresulfiding less difficult.

[0014] European patent application No. 0 506 206 also describes ahydrotreating catalyst comprising an S-containing additive selected fromthe group of bi-mercaptanes, aminosubstituted mercaptanes, andthiocarboxylic acids. The S-containing catalyst is again intended toavoid the necessity of presulfiding. Some of the catalysts described inthis reference are activated by a treatment with hydrogen at atemperature from room temperature up to 400° C., preferably 100-300° C.

[0015] Similar subject-matter is described in European patentapplication No. 0 338 788, and European patent application No. 0 289211.

[0016] U.S. Pat. No. 5,139,990 describes a hydrotreating catalystcomprising a carrier and hydrogenation metal components which is treatedwith an aqueous medium comprising a water-soluble or water-miscibleS-containing organic additive, followed by drying the resulting catalystand activating it with hydrogen at a temperature of 100-600° C.

[0017] U.S. Pat. No. 4,636,487 describes a hydrotreating catalystcomprising a support and a hydroxymercaptide of one or more metals,which may be the reaction product of a mercaptoalcohol and one or moremetal compounds. The catalyst may be activated with hydrogen at atemperature of 66-316° C.

[0018] European patent application No. 0 496 592 describes ahydrotreating catalyst comprising a carboxylic acid and an organicsulfur compound which may be a mercaptocarboxylic acid.

[0019] European patent application EP 1041133, describes effectingultra-deep HDS with a catalyst comprising an O- or N-containingadditive.

[0020] We have found that a catalyst which comprises a Group VIB metalcomponent, a Group VIII metal component, and an S-containing organicadditive is particularly efficient in reducing the sulfur content of ahydrocarbon feedstock to a value of less than about 200 ppm. Inaddition, this catalyst may make it possible to effect this ultra-deepHDS in combination with at least one of improved reduction of the amountof nitrogen, improved reduction of the total amount of aromaticspresent, and improved reduction of the amount of polynuclear aromatics.Preferably, the catalyst according to the invention shows ultra-deep HDSin combination with at least improved reduction of the amount ofnitrogen, more preferably also in combination with improved reduction ofthe total amount of aromatics present, and improved reduction of theamount of polynuclear aromatics.

SUMMARY OF THE INVENTION

[0021] Accordingly, in one embodiment, the present invention is aprocess for reducing the sulfur content of a hydrocarbon feedstockhaving an initial boiling point of not less than about 100° C. and a 95%boiling point of about 450° C. or less and a sulfur content not greaterthan about 2 wt. % to a sulfur content of less than about 200 ppm. Theinvention comprises contacting the feedstock with a catalyst comprisinga Group VIB metal component, a Group VIII metal component, and anS-containing organic additive at a temperature from about 200 to about450° C., a hydrogen partial pressure from about 5 to about 200 bar, aliquid hourly space velocity from about 0.1 to about 10 vol./vol.h andan H₂/oil ratio from about 50 to about 2000 NI/I.

[0022] In a second embodiment, the present invention comprises the abovefirst embodiment, except rather than the feedstock being contacted withthe catalyst comprising a Group VIB metal component, a Group VIII metalcomponent, and an S-containing organic additive, it is contacted withthat catalyst after the catalyst is subjected to a sulfidation stepand/or activation step.

[0023] In a third embodiment, the present invention comprises a two-stepprocess for converting a starting feedstock having an initial boilingpoint of not less than about 100° C. and a 95% boiling point of about450° C. or less and having a sulfur content of above about 0.1 wt. % andnot greater than about 2 wt. % into a product having a sulfur content ofabout 200 ppm or less. The process comprises contacting the feedstockwith a first catalyst followed by contact with a second catalyst, bothcatalysts comprising a Group VIB metal component and a Group VIII metalcomponent, with at least the second catalyst additionally comprising anS-containing organic additive. The conditions for contact with bothcatalysts may be the same or different and comprise a temperature fromabout 200 to about 450° C., a hydrogen partial pressure from about 5 toabout 200 bar, a liquid hourly space velocity from about 0.1 to about 10vol./vol.h and an H₂/oil ratio from about 50 to about 2000 NI/. Theeffluent from contact with the first catalyst has a sulfur content ofless than about 0.1 wt. %, and the product after contact with the secondcatalyst has a sulfur content of less than about 200 ppm.

[0024] A fourth embodiment of the present invention comprises the abovethird embodiment, except rather than the feedstock being contacted withcatalysts that comprise a Group VIB metal component and a Group VIIImetal component, with at least the second catalyst additionallycomprising an S-containing organic additive, the first catalyst and/orthe second catalyst are subjected to a sulfidation step and/oractivation step before contact, respectively, with the feedstock orcontact with the effluent from contact with the first catalyst.

[0025] Other objectives and embodiments of the present inventionencompass details about catalyst compositions, S-containing organicadditive and sulfur content of feedstock and product, all of which arehereinafter disclosed in the following discussion of each of the facetsof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The Additive-Containing Catalyst

[0027] In principle, the additive-containing catalyst can be anycatalyst which comprises a Group VIB hydrogenation metal and/or a GroupVIII hydrogenation metal, and an S-containing organic additive on acarrier. Catalysts comprising the combination of a Group VIBhydrogenation metal and a Group VIII hydrogenation metal are preferred.

[0028] As Group VIB metals suitable for use in the additive-containingcatalyst for use in the process according to the invention may bementioned molybdenum, tungsten, and chromium. Group VIII metals includenickel, cobalt, and iron. Catalysts comprising molybdenum as Group VIBmetal component and nickel and/or cobalt as Group VIII metal componentare preferred. For use in the process according to the inventioncatalysts comprising nickel may be preferred, especially when the feedcomprises less than about 0.1 wt. % of sulfur. The catalyst usually hasa metal content in the range of about 0.1 to about 50 wt. % calculatedas oxides on the dry weight of the catalyst not containing the additive.The Group VIB metal will frequently be present in an amount of about 5to about 40 wt. %, preferably about 15 to about 30 wt. %, calculated astrioxide. The Group VIII metal will frequently be present in an amountof about 1 to about 10 wt. %, preferably about 2 to about 7 wt. %,calculated as monoxide. The catalyst may also contain other components,such as phosphorus, halogens, and boron. Particularly, the presence ofphosphorus in an amount of about 1 to about 10 wt. %, calculated asP₂O₅, may be preferred.

[0029] The catalyst carrier may comprise the conventional oxides, e.g.,alumina, silica, silica-alumina, alumina with silica-alumina dispersedtherein, silica-coated alumina, magnesia, zirconia, boria, and titania,as well as mixtures of these oxides. As a rule, preference is given tothe carrier comprising alumina, silica-alumina, alumina withsilica-alumina dispersed therein, or silica-coated alumina. Specialpreference is given to the carrier consisting essentially of alumina oralumina containing up to about 25 wt. % of other components, preferablysilica. A carrier comprising a transition alumina, for example an eta,theta, or gamma alumina is preferred within this group, with a carriercomprising gamma-alumina being especially preferred. Additionally,although it is considered less preferred at present, the catalyst maycontain 0 to about 60 wt. % of zeolite.

[0030] The catalyst's pore volume (measured via N2 adsorption) generallyis in the range of about 0.25 to about 1 ml/g. The specific surface areawill generally be in the range of about 50 to about 400 m²/g (measuredusing the BET method). Generally, the catalyst will have a median porediameter in the range of about 7 to about 20 nm, as determined by N2adsorption. The figures for the pore size distribution and the surfacearea given above are determined after calcination of the catalyst at500° C. for one hour.

[0031] The catalyst is suitably in the form of spheres, pellets, beads,or extrudates. Examples of suitable types of extrudates have beendisclosed in the literature (see, int. al., U.S. Pat. No. 4,028,227).Highly suitable are cylindrical particles (which may be hollow or not)as well as symmetrical and asymmetrical polylobed particles (3 or 4lobes).

[0032] The additive present in the catalyst may be any S-containingorganic additive. In the context of the present specification the termorganic additive refers to an additive comprising at least one carbonatom and at least one hydrogen atom.

[0033] Preferred compounds include the mercaptocarboxylic acidsrepresented by the general formula HS—R1—COOR, wherein R1 stands for adivalent hydrocarbon group with 1 to about 10 carbon atoms and R standsfor a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium,or a linear or branched alkyl group having 1 to about 10 carbon atoms.Examples include mercaptoacetic acid (HS—CH2—COOH),beta-mercaptoproprionic acid (HS—CH2CH2—COOH), methylmercaptoacetate(HS—CH2—COOCH3), ethyl 2-mercaptoacetate (HS—CH2—COOC2H5), ethylhexylmercaptoacetate (HS—CH2-COOC8H17), and methyl 3-mercaptoproprionate(HS—CH2CH2—COOCH3). Preferred compounds also include amino-substitutedmercaptanes represented by the general formula H2N—R2—SH, wherein R2stands for a divalent hydrocarbon group having 1 to about 15 carbonatoms. Examples of these compounds include 2-amino ethanethiol(H2N—CH2CH2—SH), and 4-amino thiophenol (H2N—C6H4—SH).

[0034] Preferred compounds also include di-mercaptanes represented bythe general formula HS—R3—SH, wherein R3 stands for a divalenthydrocarbon group having 1 to about 15 carbon atoms. Examples of thesecompounds include ethanedithiol (HS—CH2CH2—SH) and 1,4-butanedithiol(HS—(CH2)4—SH). Preferred compounds also include thioacids of theformula R4—COSH, wherein R4 stands for a monovalent hydrocarbon grouphaving 1 to about 15 carbon atoms. Examples of these compounds includethioacetic acid (CH3—COSH) and thiobenzoic acid (C6H5COSH). Dithioacidsof the formula HSOC—R5—COSH wherein R5 is a divalent hydrocarbon groupwith 1 to about 15 carbon atoms may also be suitable. An example isdithioadipic acid (HSOC—C4H10—COSH). Preferred compounds also includemercaptoalcohols of the general formula R6S—R5—(OH)n, wherein R5represents an alkyl group having from 1 to about 15 carbon atoms or aphenyl group, R6 represents a hydrogen atom or an alkyl group having 1or about 2 carbon atoms, and n is 1 or about 2. Examples of thesecompounds include 2-mercaptoethanol, 2-(methylthio)ethanol,2-(ethylthio)ethanol, 3-mercapto-2-butanol, 4-mercaptophenol,2-(methylthio)phenol, 4-(methylthio)phenol, 2-(ethylthio)phenol,3-mercapto-1,2,-propanediol, 3-methylthio-1,2, propanediol, and3-ethylthio-1,2, propanediol. Other suitable compounds includesulfoxides of the formula R7—SO—R8, wherein R7 and R8 are hydrocarbongroups with 1 to about 5 carbon atoms. An example is dimethyl sulfoxide(CH3—SO—CH3).

[0035] Ammonium thiocyanate and thiourea may also be useful compounds,as may be the various dithiocarbamic acids and the salts thereof, suchas ethylene bisdithiocarbamic acid and its salts, and dimethyldithiocarbamic acid and its salts. Other suitable compounds includemercaptodiathiazoles and their salts, such as2,5-dimercapto-1,3,4,-diathiazoles and its salts.

[0036] Other compounds which may be useful are (poly)sulfides of theformula R9—Sx—R10, wherein x is a value of 1 to about 15 and R9 and R10are alkyl groups, preferably branched alkyl groups, with 1 to about 30carbon atoms. Related compounds are those with the formulaHO—R11—Sx—R12—OH, wherein x is a value of 1 to about 15 and R11 and R12are alkyl groups with 1 to about 8 carbon atoms.

[0037] At this point in time the mercaptocarboxylic acids are consideredpreferred for reasons of activity. Other compounds, in particularlythose that are soluble in or miscible with water, may be preferred forenvironmental reasons (less odour and/or no organic solvent necessary).

[0038] A single compound as well as a combination of compounds may beused as additive.

[0039] The amount of additive present in the additive-containingcatalyst depends on the specific situation. It was found that theappropriate amount of additive generally lies in the range of about 0.01to about 2.5 moles of additive per mole of hydrogenation metals presentin the catalyst. If the amount of additive added is too low, theadvantageous effect associated with its presence will not be obtained.On the other hand, the presence of an exceptionally large amount ofadditive will not improve its effect. Generally, the aim is to selectthe amount of sulfur incorporated into the catalyst by way of theadditive to correspond to about 5 to about 200%, preferably about 50 toabout 200%, more preferably about 80 to about 150%, of thestoichiometric sulfur quantity necessary to convert the hydrogenationmetals into Co₉S₈, MoS₂, WS₂, and Ni₃S₂, respectively.

[0040] The way in which the additive is incorporated into the catalystcomposition is not critical to the process according to the invention.The additive may be incorporated into the catalyst composition prior to,subsequent to, or simultaneously with the incorporation of thehydrogenation metal components.

[0041] For example, the additive can be incorporated into the catalystcomposition prior to the hydrogenation metal components by being addedto the carrier before the hydrogenation metal components are. This canbe done by mixing the additive with the carrier material before it isshaped, or by impregnating the shaped carrier material with theadditive. This embodiment is not preferred at this point in time.

[0042] Alternatively, the additive can be incorporated into the catalystcomposition simultaneously with the hydrogenation metal components. Thiscan be done, e.g., by mixing the additive and the hydrogenation metalcomponents with the carrier material before shaping or by impregnatingthe carrier with an impregnation solution comprising the hydrogenationmetal components and the additive, followed by drying under suchconditions that at least part of the additive is maintained in thecatalyst.

[0043] It is also possible to incorporate the additive into the catalystcomposition subsequent to the hydrogenation metal components. This canbe done, e.g., by first incorporating the hydrogenation metal componentsinto the catalyst composition, e.g., by mixing them with the carriermaterial or by impregnating the carrier with them, optionally followedby drying and/or calcining, and subsequently incorporating the additive,e.g., by impregnation.

[0044] Depending on the nature of the additive and the way in which itis incorporated into the catalyst composition, the additive may be usedin the solid form, in the liquid form, or dissolved in a suitablesolvent. It may be preferred for the additive to be incorporated intothe catalyst dissolved in water.

[0045] The catalyst may be activated by contacting it with hydrogen at atemperature of about 100 to about 600° C. as described in, e.g., EP 0506 206, EP 0 338 788, EP 0 289 211, U.S. Pat. No. 4,636,487, and U.S.Pat. No. 5,139,990. Optionally, the catalyst may be contacted with anorganic liquid either prior to or simultaneously with the contactingwith hydrogen. Such a process is the subject of U.S. patent applicationSer. No. 09/8296525, filed Apr. 10, 2001, which is incorporated hereinby reference.

[0046] If so desired, the catalyst may be subjected to a sulfiding stepbefore its use in effecting ultra-deep HDS, said sulfiding step takingplace ex situ, in situ or in a combination of ex situ and in situ. Inthe context of the present specification, the indication sulfiding stepor sulfidation step is meant to include any process step in which asulfur-containing compound is added to the catalyst composition and inwhich at least a portion of the hydrogenation metal components presentin the catalyst is converted into the sulfidic form, either directly orafter an activation treatment with hydrogen.

[0047] Suitable sulfidation processes are known in the art. Ex situsulfidation processes take place outside the reactor in which thecatalyst is to be used in hydrotreating hydrocarbon feeds. In such aprocess the catalyst is contacted with a sulfur compound, e.g. apolysulfide or elemental sulfur, outside the reactor and, if necessary,dried. In a second step, the material is treated with hydrogen gas atelevated temperature in the reactor, optionally in the presence of afeed, to activate the catalyst, i.e. bring it into the sulfided state.

[0048] In situ sulfidation processes take place in the reactor in whichthe catalyst is to be used in hydrotreating hydrocarbon feeds. Here, thecatalyst is contacted in the reactor at elevated temperature with ahydrogen gas stream mixed with a sulfiding agent, such as hydrogensulfide or a compound, which under the prevailing conditions isdecomposable into hydrogen sulfide. It is also possible to use ahydrogen gas stream combined with a hydrocarbon feed comprising a sulfurcompound that under the prevailing conditions is decomposable intohydrogen sulfide. In the latter case it is possible to use a hydrocarbonfeed comprising an added sulfiding agent (a so-called spiked feed), butit is also possible to use a sulfur-containing hydrocarbon feed withoutany added sulfiding agent, since the sulfur components present in thefeed will be converted into hydrogen sulfide in the presence of thecatalyst. The hydrocarbon feed may be the feed to be subjected toultra-deep HDS in the process according to the invention, but it mayalso be a different feed, later to be replaced with the feed to besubjected to ultra-deep HDS. Combinations of the various sulfidingtechniques may also be applied. In the context of the present inventionit may be preferred to sulfide the catalyst by contacting it with an,optionally spiked, hydrocarbon feed.

[0049] A further process for presulfiding catalysts comprising anorganic S-containing catalyst is the subject of U.S. patent applicationSer. No. 09/829,626, filed Apr. 10, 2001, which is incorporated hereinby reference. This patent application is directed to a presulfidingprocess in which a catalyst comprising a sulfur-containing additive ispresulfided in two steps, the first step being carried out at a lowertemperature than the second step. U.S. patent application Ser. No.09/829,640, filed Apr. 10, 2001, which is incorporated herein byreference, also describes a suitable presulfiding procedure forcatalysts containing an S-containing additive. In the process describedin this reference the presulfiding is carried out ex-situ.

[0050] Another process, which may be preferred over those of the twoabove-mentioned references is described in U.S. patent application Ser.No. 09/829,624, filed Apr. 10, 2001, which is also incorporated hereinby reference. This patent application is directed to a presulfidingprocess in which a catalyst comprising a sulfur-containing additive isfirst contacted with an organic liquid followed by being contacted withhydrogen and a sulfur-containing compound in the gaseous phase.

[0051] The Feed

[0052] The feedstock suitable for use in the process according to theinvention has a 95% boiling point, as determined in accordance with ASTMD-2887, of about 450° C. or less, preferably about 420° C. or less, morepreferably about 400° C. or less. That is, 95 vol.% of the feedstockboils at a temperature of about 450° C. or less, preferably about 420°C. or less, more preferably about 400° C. or less. Generally, theinitial boiling point of the feedstock is not less than about 100° C.,preferably not less than about 180° C.

[0053] The feedstock to be used in the process according to theinvention may or may not have been subjected to a previoushydrodesulfurisation step, depending on the envisaged processconditions.

[0054] If the reaction conditions can be selected suitable for moresevere hydrotreating, the catalyst used in the process of the inventionis sufficiently active to be able to convert fractions with a sulfurcontent of, e.g., about 0.1 wt. % ppm to about 2 wt. %, preferably 1 toabout 2 wt. %, into product with a sulfur content less than about 200ppm, preferably less than about 100 ppm, more preferably, less thanabout 50 ppm. Such feedstocks generally contain about 20 to about 1200ppm nitrogen, preferably about 30 to about 800 ppm, more preferablyabout 70 to about 600 ppm. The metal content of such feedstockspreferably is less than about 5 ppm, more preferably less than about 1ppm (Ni+V). Examples of suitable feedstocks of this type are feedstockscomprising one or more of straight run gas oil, light catalyticallycracked gas oil, and light thermally cracked gas oil, and (mild)hydrocracked oils.

[0055] On the other hand, the invention is also suitable for theultra-deep hydrodesulfurisation of hydrocarbon feeds of the abovedescription which had already been subjected to a hydrotreatingoperation, and which have sulfur contents of generally less than about0.1 wt. %, more specifically about 150 to about 500 ppm. [Obviously,applying the process according to the invention to feeds with a sulfurcontent less than about 200 ppm will only be useful if a sulfur contentbelow that value is desired, e.g., less than about 100 ppm, or less thanabout 50 ppm.]

[0056] If it is desired to subject the above-mentioned startinghydrocarbon feedstock to a first hydrotreating (hydrodesulfurisation)step to reduce its sulfur content to a value less than about 0.1 wt. %,this can be carried out in various ways. One can, e.g., use aconventional hydrodesulfurisation catalysts comprising a Group VIB metalcomponent, a Group VIII metal component, and, optionally, phosphorus ona carrier comprising alumina. Suitable hydrodesulfurisation catalystsare commercially available, and include for example KF 756 and KF 901 ofAkzo Nobel. It is also possible to effect such firsthydrodesulfurisation step by means of a two-step process, such as thosedescribed in EP 0 464 931, EP-A 0 523 679 or EP 870 807. If so desired,one may also use an additive-based catalyst to effect such firsthydrodesulfurisation step.

[0057] The present invention also pertains to a two-step process forconverting a starting feedstock having a sulfur content of above about0.1 wt. % into a product having a sulfur content of less than about 200ppm, wherein the process comprises optionally sulfiding and/oractivating a first and a second catalyst comprising a Group VIB metalcomponent and a Group VIII metal component, with at least the secondcatalyst additionally comprising an S-containing organic additive,contacting a feedstock with a 95% boiling point of about 450° C. or lessand a sulfur content of about 0.1 wt. % or more with the first catalystunder conditions of elevated temperature and pressure to form a productwith a sulfur content of less than about 0.1 wt. %, preferably less thanabout 500 ppm, and contacting the effluent from the first catalyst,optionally after fractionation or intermediate phase separation, withthe second catalyst under conditions of elevated temperature andpressure to form a product with a sulfur content of less than about 200ppm, preferably less than about 100 ppm, more preferably less than about50 ppm.

[0058] It is considered preferred at this point in time for the firstcatalyst to comprise molybdenum as Group VIB metal component and cobaltand/or nickel as Group VIII metal component, with the second catalystcomprising molybdenum as Group VIB metal component and nickel as GroupVIII metal component. The two-step process can be carried out in one ortwo reactors, as may be desired. If both catalysts contain an organicadditive, the two catalysts may be the same or different.

[0059] The Process Conditions

[0060] The process according to the invention is carried out at elevatedtemperature and pressure. The temperature generally is about 200 toabout 450° C., preferably about 280 to about 430° C. The reactor inlethydrogen partial pressure generally is about 5 to about 200 bar,preferably about 10 to about 100 bar, more preferably about 15 to about60 bar. The liquid hourly space velocity preferably is between about 0.1and about 10 vol./vol.h, more preferably between about 0.5 and about 4vol./vol.h. The H₂/oil ratio generally is in the range of about 50 toabout 2000 NI/I, preferably in the range of about 80 to about 1000 NI/I.For the two-step process described above, the reaction conditions forboth steps may be selected independently from each other, taking theabove-mentioned general and preferred ranges into account.

[0061] The process conditions are selected in such a way that the sulfurcontent of the total liquid effluent is less than about 200 ppm,preferably less than about 100 ppm, more preferably less than about 50ppm. The exact process conditions will depend, int. al., on the natureof the feedstock, the desired degree of hydrodesulfurisation, and thenature of the catalyst. In general, a higher temperature, a higherhydrogen partial pressure, and a lower space velocity will decrease thesulfur content of the final product. The selection of the appropriateprocess conditions to obtain the desired sulfur content in the productis well within the scope of the person skilled in the art ofhydroprocessing.

EXAMPLE 1

[0062] Preparation of Additive-Containing Catalyst

[0063] Extrudates of a gamma-alumina carrier were impregnated to porevolume saturation with an impregnation solution comprising a molybdenumcompound, a nickel compound, and phosphoric acid, after which theimpregnated carrier was dried at a temperature of 140° C. for a periodof 16 hours. The dried extrudates were impregnated with a solution ofthioglycolic acid (TGA), and dried. The final catalyst contained 20 wt.% of molybdenum, calculated as trioxide, 5 wt. % of nickel, calculatedas oxide, and 7 wt. % of phosphorus, calculated as P₂O₅. All weightpercentages are calculated on the dry catalyst base, not including theadditive. The molar ratio between TGA and the total of Ni and Mo is 0.4.

[0064] The catalyst according to the invention was tested in an upflowtubular reactor side by side with commercial catalyst KF 756 of AkzoNobel. Each reactor tube contained 75 ml of catalyst homogeneouslyintermixed with 70 ml of carborundum particles. The catalysts weresulfided using the feed specified below in which dimethyl disulfide hadbeen dissolved to a total S content of 2.5 wt. %.

[0065] The feed applied was a Kuwait petroleum gas oil feedstock withthe following properties. Nitrogen (ASTM D-4629) 86 (ppmwt) Sulfur (ASTMD-4294) (ppmwt) 1.2 wt. % Density 15° C. (g/ml) 0.84 Dist. (° C.) ASTMD-86 IBP 184 5 vol. % 219 10 vol. % 231 30 vol. % 265 50 vol. % 287 70vol. % 310 90 vol. % 345 95 vol. % 360 FBP 373

[0066] The catalysts were tested under the two test conditions givenbelow. Condition 1 Condition 2 pressure (bar) 40 20 Temperature (° C.)330 340 LHSV (h-1) 2 1.5 H₂/oil ratio (NI/I) 300 300

[0067] The products from the different runs were analysed. The resultsthereof are given below. Condition 1 Catalyst according Comparative tothe invention catalyst product S (ppm) 21 279 product N (ppm) 0.9 14

[0068] Condition 2 Catalyst according Comparative to the inventioncatalyst product S (ppm) 51 132 product N (ppm) 5 35

[0069] This example shows that the catalyst according to the inventionwhich contains an S-containing additive gives a much lower S and N levelin the final product than the comparative commercial catalyst.

1. A process for reducing the sulfur content of a hydrocarbon feedstockhaving an initial boiling point of not less than about 100° C. and a 95%boiling point of about 450° C. or less and a sulfur content not greaterthan about 2 wt. % to a sulfur content of less than about 200 ppm,comprising contacting said feedstock with a catalyst comprising a GroupVIB metal component, a Group VIII metal component, and an S-containingorganic additive at a temperature from about 200 to about 450° C., ahydrogen partial pressure from about 5 to about 200 bar, a liquid hourlyspace velocity from about 0.1 to about 10 vol./vol.h and an H₂/oil ratiofrom about 50 to about 2000 NI/I.
 2. The process of claim 1, wherein thesulfur content of the product is less than about 50 ppm.
 3. The processof claim 1, wherein the S-containing organic additive is amercaptocarboxylic acid represented by the general formula HS—R1—COOR,wherein R1 stands for a divalent hydrocarbon group with 1 to about 10carbon atoms and R stands for a hydrogen atom, an alkali metal, analkaline earth metal, ammonium, or a linear or branched alkyl grouphaving 1 to about 10 carbon atoms.
 4. The process of claim 1, whereinthe sulfur content of the feedstock is between about 150 ppm and about 2wt. %.
 5. The process of claim 4, wherein the sulfur content of thefeedstock is between about 0.1 wt. % and about 2 wt. %.
 6. The processof claim 4, wherein the sulfur content of the feedstock is between about150 ppm and about 500 ppm.
 7. The process of claim 1, wherein saidfeedstock is contacted with said catalyst at a temperature from about280 to about 430° C.
 8. The process of claim 1, wherein said hydrogenpartial pressure is from about 10 to about 100 bar.
 9. The process ofclaim 1, wherein said hydrogen partial pressure is from about 15 toabout 60 bar.
 10. The process of claim 1, wherein said liquid hourlyspace velocity is from about 0.5 to about 4 vol./vol.h.
 11. The processof claim 1, wherein said H₂/oil ratio is from about 80 to about 1000NI/I.
 12. A process for reducing the sulfur content of a hydrocarbonfeedstock having an initial boiling point of not less than about 100° C.and a 95% boiling point of about 450° C. or less and a sulfur contentnot greater than about 2 wt. % to a sulfur content of less than about200 ppm, comprising contacting said feedstock with a catalyst at atemperature from about 200 to about 450° C., a hydrogen partial pressurefrom about 5 to about 200 bar, a liquid hourly space velocity from about0.1 to about 10 vol./vol.h and an H₂/oil ratio from about 50 to about2000 NI/l, said catalyst comprising a Group VIB metal component, a GroupVIII metal component, and an S-containing organic additive, saidcatalyst being subjected to a sulfidation step and/or activation stepbefore contact with said feedstock.
 13. The process of claim 12, whereinthe sulfur content of the product is less than about 50 ppm.
 14. Theprocess of claim 12, wherein the S-containing organic additive is amercaptocarboxylic acid represented by the general formula HS—R1—COOR,wherein R1 stands for a divalent hydrocarbon group with 1 to about 10carbon atoms and R stands for a hydrogen atom, an alkali metal, analkaline earth metal, ammonium, or a linear or branched alkyl grouphaving 1 to about 10 carbon atoms.
 15. The process of claim 12, whereinthe sulfur content of the feedstock is between about 150 ppm and about 2wt. %.
 16. The process of claim 15, wherein the sulfur content of thefeedstock is between about 0.1 wt. % and about 2 wt. %.
 17. The processof claim 15, wherein the sulfur content of the feedstock is betweenabout 150 ppm and about 500 ppm.
 18. The process of claim 12, whereinsaid feedstock is contacted with said catalyst at a temperature fromabout 280 to about 430° C.
 19. The process of claim 12, wherein saidhydrogen partial pressure is from about 10 to about 100 bar.
 20. Theprocess of claim 12, wherein said hydrogen partial pressure is fromabout 15 to about 60 bar.
 21. The process of claim 12, wherein saidliquid hourly space velocity is from about 0.5 to about 4 vol./vol.h.22. The process of claim 12, wherein said H₂/oil ratio is from about 80to about 1000 NI/I.
 23. A two-step process for converting a startingfeedstock having an initial boiling point of not less than about 100° C.and a 95% boiling point of about 450° C. or less and having a sulfurcontent of above about 0.1 wt. % and not greater than about 2 wt. % intoa product having a sulfur content of about 200 ppm or less, wherein theprocess comprises contacting said feedstock with a first catalystfollowed by contact with a second catalyst, both catalysts comprising aGroup VIB metal component and a Group VIII metal component, with atleast said second catalyst additionally comprising an S-containingorganic additive, the conditions for said contact with both catalystsbeing the same or different and comprising a temperature from about 200to about 450° C., a hydrogen partial pressure from about 5 to about 200bar, a liquid hourly space velocity from about 0.1 to about 10vol./vol.h and an H₂/oil ratio from about 50 to about 2000 NI/I, theeffluent from contact with said first catalyst having a sulfur contentof less than about 0.1 wt. %, and the product after contact with thesecond catalyst having a sulfur content of less than about 200 ppm. 24.The process of claim 23, wherein the effluent following contact withsaid first catalyst is contacted with said second catalyst afterfractionation or intermediate phase separation.
 25. The process of claim23 wherein the first catalyst comprises molybdenum as Group VIB metalcomponent and cobalt and/or nickel as Group VIII metal component, whilethe second catalyst comprises molybdenum as Group VIB metal componentand nickel as Group VIII metal component.
 26. A two-step process forconverting a starting feedstock having an initial boiling point of notless than about 100° C. and a 95% boiling point of about 450° C. or lessand having a sulfur content of above about 0.1 wt. % and not greaterthan about 2 wt. % into a product having a sulfur content of about 200ppm or less, wherein the process comprises contacting said feedstockwith a first catalyst followed by contact with a second catalyst, theconditions for said contact with both catalysts being the same ordifferent and comprising a temperature from about 200 to about 450° C.,a hydrogen partial pressure from about 5 to about 200 bar, a liquidhourly space velocity from about 0.1 to about 10 vol./vol.h and anH₂/oil ratio from about 50 to about 2000 NI/I, the effluent from contactwith said first catalyst having a sulfur content of less than about 0.1wt. %, and the product after contact with the second catalyst having asulfur content of less than about 200 ppm, both of said catalystscomprising a Group VIB metal component and a Group VIII metal component,with at least said second catalyst additionally comprising anS-containing organic additive, said first catalyst and/or said secondcatalyst being subjected to a sulfidation step and/or activation stepbefore contact, respectively, with said feedstock or contact with theeffluent from contact with said first catalyst.
 27. The process of claim26, wherein the effluent following contact with said first catalyst iscontacted with said second catalyst after fractionation or intermediatephase separation.
 28. The process of claim 26 wherein the first catalystcomprises molybdenum as Group VIB metal component and cobalt and/ornickel as Group VIII metal component, while the second catalystcomprises molybdenum as Group VIB metal component and nickel as GroupVIII metal component.